Re: Dreaming About Redesigning SQL

"Marshall Spight" <mspight_at_dnai.com> wrote in message news:vTwmb.26460$HS4.96761_at_attbi_s01...
> "Bob Badour" <bbadour_at_golden.net> wrote in message
news:DMSdnQAx4NQUGweiU-KYhA_at_golden.net...
> > >
> > > > In general, though, a table with no parent and no child is of little
> > > > use. It must contain information that has no relevance to any other
> > > > information in the database. Can you give an example or two of such
> > > > a table?
> >
> > Dee, Dum, Integer. Is three enough or is it too many?
>
> Two of those relation names are so obscure that he's never
> going to be able to figure out what you mean. I did a Google
> search for "Dee" and the first hit was about Dee Schneider,
> ha ha! "table dee" fared no better.
>
> "Dee" is the relation of zero attributes and one row. "Dum"
> is the relation of zero attributes and zero rows. (I don't
> think they're very good names, either, but at least they
> have a rare tad of whimsy in them.)
>
> These relations are useful and interesting in much the
> same way 1 and 0 are useful integers:
>
> relation X join Dee = Dee <-- error here: should equal X
> relation X JOIN Dum = Dum <-- empty relation same type as X
>
> Cool, eh?

Even cooler, these relations are useful and interesting in exactly the same way True and False are useful booleans:

(X <AND> Dee){} = X{}
(X <AND> Dum){} = Dum

(X <OR> Dee){} = Dee
(X <OR> Dum){} = X{}

where {...} indicates project over the set of columns named in place of the ellipsis and where <AND> and <OR> are the operations specified in Date's and Darwen's relational algebra, A. Received on Sat Oct 25 2003 - 17:35:34 CDT